PB1768: MICRORNA SIGNATURES IMPLY A ROLE FOR FOXO IN AML CHEMO-RESISTANCE
Authors: Paula Reichelt, Stephan Bernhart, Sebanstian Schwind, Gerhard Behre, Uwe Platzbecker, Michael Cross
Journal: HemaSphere (2023)

Topic: 3. Acute myeloid leukemia - Biology & Translational Research Background: Established treatments for AML include more traditional cytotoxic regimens based on cytarabine (ARA-C) and additional targeted therapy with tyrosine kinase inhibitors (TKI). While both are effective at inducing remission, drug resistance leading to relapse remains a major problem. A better understanding of the mechanisms contributing to drug resistance will be required for the design of strategies for avoiding or combatting resistance and reinstating drug-sensitivity. Expression studies based solely on mRNA level are of limited value, due to the low correlation between mRNA and protein level. In contrast, microRNAs typically coordinate gene expression programmes post transcriptionally by affecting both turnover and translation of functionally related groups of mRNAs. Aims: The aim of this project was to use changes in microRNA signatures between drug-sensitive and -resistant AML cells to identify pathways that contribute to resistance. Methods: MicroRNA expression profiles were analyzed by NGS (next generation sequencing) of small RNAs from two cell line models of chemoresistance and from sequential primary samples of AML patient bone marrow mononuclear cells taken pre-treatment and post relapse (n = 4). The cell line models used for this study were HL60/HL60R (sensitive/resistant to ARA-C) and MV411/MV411R (sensitive/resistant to the TKI Midostaurin (PKC-412)). Bioinformatical identification of candidate deregulated pathways was performed using miRTarbase and stringdb. Protein expression and subcellular localization were assessed by western blotting and immunocytochemical staining respectively. To validate changes in pathway activity in patient samples, gene expression of well characterized target genes was assessed by qPCR. Results: In both cell line models of resistance, our microRNA based bioinformatic approach predicted more than 20 KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways to be represented differentially between resistant and sensitive cells (FDR<0.05). The FoxO signaling pathway was a predicteded target of differentially expressed microRNAs in both resistant cell lines. Protein analysis confirmed significant differences in FoxO3A expression and nuclear translocation between ARA-C resistant and ARA-C sensitive cells. A similar analysis of paired bone marrow samples from AML patients at diagnosis and first relapse also predicted FoxO signaling to be one of the most significantly affected of 11 KEGG pathways in the class of signal transduction. Gene expression analysis in patient samples confirmed relapse to be associated with higher expression of FoxO1 and FoxO target genes GADD45A and MnSOD. Consistent differences were also observed between risk groups of AML patients of the TCGA (The cancer genome atlas) dataset for the expression of FoxO target genes MnSOD and Catalase. Summary/Conclusion: Here we show that microRNA profiling can identify pathways implicated in treatment resistance in AML. A comprehensive understanding of treatment resistance should facilitate early detection as well as the development of strategies for avoiding or reversing drug-resistance. Keywords: Drug resistance, Acute myeloid leukemia, Ara-C (cytarabine)